After an upgrade of gtk+ to 2.18.4 through the normal FreeBSD
port/package I noticed that there is a problem with range widgets
and the mouse wheel.

When I *reduce* the value of a range widget by rolling the mouse
wheel backwards, all works fine.  Increasing the value by rolling
the wheel 'forward' or 'up' (for horizontal widgets) does not
update the value of the range widget at all.

This is easy to repeat here by clicking on the icon of the volume
control applet in Gnome [gnome-volume-control-applet] and trying
to adjust the master volume using the mouse wheel.  Lowering the
volume works.  Bumping it to a higher value doesn't work at all.

Other range widgets, even horizontal ones, e.g. in the Gnome
volume preferences dialog, also show the same problem.